Implants are known which measure electrode impedances, sensing amplitudes, pacing thresholds, or sensing signal patterns in order to check the electrode integrity. However, the known methods are not sensitive enough to detect all electrode faults as early as the initial stage, i.e. to detect electrode faults at a point in time when the therapy and diagnostic functions are not yet limited.
In Farwell et al., “Inappropriate implantable cardioverter defibrillator shocks in fractured Sprint Fidelis leads associated with ‘appropriate’ interrogation,” Europace (2008) 10(6), 726-728, a case study of a defective electrode system is described, in which electromagnetic irradiation of the programmer telemetry results in inadequate shock delivery. The cited publication describes very clearly the coupling of an electromagnetic wave by a programmer device into a defective electrode system that previously showed no signs of defects. In this case the coil telemetry of the programmer device results in a typical coupling into the electrode lead which functions as an antenna. Since the defect present in the electrode lead has resulted in a permanent change to the antenna characteristic of the electrode lead in the system, this coupling is sensed as an arrhythmia signal by the electronic implant, and a shock is delivered. In contrast, if the electrode lead is intact, the irradiation of the programmer telemetry does not produce interfering signals in the input stage of the ICD.